In a cement calcination plant, a large amount of waste heat of a suspension preheater (hereinafter, may be referred to as just a preheater or a PH) and waste heat of an air quenching cooler (hereinafter, may be referred to as just a quenching cooler or AQC) is discharged, so that a waste heat boiler generates steam by using the waste heat so as to drive a steam turbine by the steam, thereby generates power.
On the other hand, in the cement calcination plant, there are two waster heat sources, namely, the preheater and air quenching cooler. The waste gas temperature and waste heat quantity are greatly different between the two heat sources and vary with the operation condition of the plant, so that the heat quantity supply due to both waste heats is not always stable.
The waste gas temperature of the preheater (PH) is, for example, 350 to 400° C., and the waste gas temperature of the air quenching cooler (AQC) is almost 300 to 250° C. A conventional waste heat power generation system for generating high-pressure steam has been operated so far, so as to generate high pressure steam by the boilers using the waste heat, that is, a PH boiler and an AQC boiler. The exit gas temperature of the PH boiler is set at 250° C. or so, so that the cement raw materials are dried using the heat. On the other hand, the AQC waste heat is collected by the AQC boiler to its limit, thereby generating electric power.
[Related Art 1]
The embodiment of the waste heat power generation system aforementioned varies with the productivity and the way of using the residual heat of a cement calcination plant to which the embodiment is applied. There is a waste heat power generation system (Related Art 1) that the steam turbine is used as a multi-staged mixed pressure turbine, and high-pressure steam is generated by the PH boiler and is introduced into the high-pressure stage of the steam turbine. On the other hand, low-pressure steam is generated by hot water of the AQC heater and is introduced into the low-pressure stage of the steam turbine. Thus the steam turbine is driven (FIG. 4 of JP-A 58-57013). The outline thereof is as shown in FIG. 2. The waste heat power generation system heats condensate of a condenser C by an economizer h of an AQC heater 50, introduces low-pressure steam generated by a flasher F into a low-pressure stage Pb of a steam turbine T. On the other hand, this system heats condensate of the condenser C by an evaporator h-2 of a PH boiler 40, superheats it by a superheater h-1, and introduces the same into a high-pressure stage Pa of the steam turbine T. The steam pressure of low-pressure steam by the AQC heater 50 of this waste heat power generation system is about 3 atg, and the temperature of exit gas B2 of the heater is about 100° C. The steam pressure of high-pressure steam by the PH heater 40 is about 16 atg, and the temperature of exit gas B1 of the boiler is about 230° C.
[Related Art 2]
As an embodiment of the waste heat power generation system for increasing the waste heat recovery rate of the air quenching cooler (AQC), there is a waste heat power generation system (Related Art 2) that a part of hot water heated by the economizer h of the AQC heater 50 is introduced into the flasher F to form low-pressure steam, and it is introduced into the low-pressure stage Pb of the steam turbine T. And, another one part of the aforementioned hot water is superheated by the PH boiler, and it is introduced into the high-pressure stage Pa of the steam turbine T (FIG. 3 of JP-A 58-49801).
The outline of the system of Related Art 2 is as shown in FIG. 3. This system of Related Art 2 heats condensate of the condenser C by the economizer h of the AQC heater 50, introduces a part of the hot water into the flasher F, and introduces the low-pressure steam into the low-pressure stage Pb of the steam turbine T. On the other hand, this system heats another one part of the hot water by the evaporator h-2 of the PH boiler, furthermore superheats it by the superheater h-1, and introduces the same into the high-pressure stage Pa of the steam turbine T.
The steam pressure of low-pressure steam by the AQC heater 50 is about 3 atg, and the temperature of exit gas B2 of the heater is about 100° C. The steam pressure of high-pressure steam by the PH heater 40 is about 16 atg, and the temperature of exit gas B1 of the boiler is about 230° C.
[Related Art 3]
Furthermore, Related Art 3 is a waste heat power generation system for increasing the waste heat recovery rate of Related Art 2 aforementioned as much as possible by adopting AQC boiler instead of AQC heater, and lowering the temperature of exit gas of the AQC boiler.
The outline thereof is as shown in FIG. 4. The waste heat power generation system is equipped with an economizer h-5, an evaporator h-4, and a superheater h-3 in an AQC boiler 50A. A part of hot water by the economizer h-5 of the AQC boiler 50A is introduced into the flasher F, and the low-pressure steam thereof is introduced into the low-pressure stage Pb of the steam turbine T. On the other hand, another one part of the hot water is introduced into the evaporator h-4 of the AQC boiler 50A, furthermore it is superheated by the superheater h-3, and the high-pressure steam is introduced into the high-pressure stage Pa of the steam turbine T. Further, still another one part of the aforementioned hot water is introduced into an evaporator h-2 of the PH boiler 40 via a valve v and an evaporator SD, then it is superheated by a superheater h-1, and the high-pressure steam is introduced into the high-pressure stage Pa of the steam turbine T.
In the economizer h-5 of the AQC boiler 50A of Related Art 3, in addition to the AQC boiler and PH boiler, by exchanging the heat of hot water for flasher, the temperature of exit gas of the AQC boiler 50A is lowered to about 100° C., so that the AQC waste heat is recovered sufficiently.
On the other hand, the high-pressure steam, which has been heated by the evaporator h-2 of the PH boiler 40 and furthermore superheated by the superheater h-1, is controlled at about 16 to 17 atg and the temperature of the exit gas B1 of the PH boiler in this case is lowered to about 230 to 200° C. And, the high-temperature exhaust gas is additionally used to dry cement raw materials.
In the cement calcination plant, in correspondence with a sudden rise of energy expenses, the power expenses rise suddenly, so that it is requested to recover this waste heat as power as much as possible. Therefore, to further increase the power generation, there is a possibility that it may be necessary to lower the temperature of exit gas of the PH boiler to about 160° C., and for that purpose, it may be considered to form a multi-pressure PH boiler.
On the other hand, in Related Art 3 aforementioned, it is important to increase the waste heat recovery rate of the preheater (PH) and air quenching cooler (AQC), so that it is important to realize a multi-pressure PH boiler, lower the exit gas temperature, increase the PH waste heat recovery rate, and maintain the waste heat recovery rate of AQC exhaust gas on a high level.